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Cisco IOS Software Releases 12.2 SB

BGP Support for Sequenced Entries in Extended Community Lists

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BGP Support for Sequenced Entries in Extended Community Lists

Table Of Contents

BGP Support for Sequenced Entries in Extended Community Lists

Contents

How to Sequence Extended Community Lists

Configuring Extended Community-list Sequencing

IP Extended Community-list Configuration Mode

Default Sequence Numbering

Resequencing Extended Community-lists

Restrictions

Verifying Extended Community-list Sequences

Configuration Examples for Sequenced Entries in Extended Community-lists

Sequenced Extended Community-list Entry Configuration: Example

Resequenced Extended Community-list Entry Configuration: Example

Sequenced Extended Community-list Entry Verification: Example

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Command Reference

ip extcommunity-list

show ip extcommunity-list


BGP Support for Sequenced Entries in Extended Community Lists


This feature introduces automatic sequencing of individual entries in Border Gateway Protocol (BGP) extended community lists. This feature also introduces the ability to remove or resequence extended community list entries without deleting the entire existing extended community list.

Feature History for the BGP Support for Sequenced Entries in Extended Community Lists Feature

Release
Modification

12.2(25)S

This feature was introduced.

12.3(11)T

This feature was integrated into Cisco IOS Release 12.3(11)T.

12.2(27)SBC

This feature was integrated into Cisco IOS Release 12.2(27)SBC.


Finding Support Information for Platforms and Cisco IOS Software Images

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Contents

How to Sequence Extended Community Lists

Configuration Examples for Sequenced Entries in Extended Community-lists

Additional References

Command Reference

How to Sequence Extended Community Lists

This section contains the following tasks:

Configuring Extended Community-list Sequencing

Verifying Extended Community-list Sequences

Configuring Extended Community-list Sequencing

Perform this task to sequence and resequence extended community lists.

IP Extended Community-list Configuration Mode

This feature introduces IP Extended community-list configuration mode. Both named and numbered extended community lists can be configured in IP Extended community-list configuration mode. To enter IP Extended community-list configuration mode, the ip extcommunity-list command is entered with either the expanded or standard keyword followed by the extended community-list name. This configuration mode supports all of the functions that are available in global configuration mode. In addition, you can perform the following operations:

Configure sequence numbers for extended community list entries

Resequence existing sequence numbers for extended community list entries

Configure an extended community list to use default values

Default Sequence Numbering

Extended community list entries start with the number 10 and increment by 10 for each subsequent entry when no sequence number is specified, when default behavior is configured, and when an extended community list is resequenced without specifying the first entry number or the increment range for subsequent entries.

Resequencing Extended Community-lists

Extended community-list entries are sequenced and resequenced on a per-extended community-list basis. The resequence command can be used without any arguments to set all entries in a list to default sequence numbering. The resequence command also allows you to set the sequence number of the first entry and increment range for each subsequent entry. The range of configurable sequence numbers is from 1 to 2147483647.

Restrictions

A sequence number is applied to all extended community-list entries by default regardless of the configuration mode. Explicit sequencing and resequencing of extended community list entries can only be configured in IP Extended community-list configuration mode and not in global configuration mode.

SUMMARY STEPS

1. enable

2. configure terminal

3. ip extcommunity-list {expanded-list-number | expanded list-name | standard-list-number | standard list-name }

4. [sequence-number] { deny [regular-expression] | exit | permit [regular-expression] | resequence [starting-sequence] [sequence-increment]}

5. [sequence-number] {deny [rt extcom-value] [soo extcom-value] | exit | permit [rt extcom-value] [soo extcom-value] | resequence [starting-sequence] [sequence-increment] }

6. end

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

ip extcommunity-list {expanded-list-number | expanded list-name | standard-list-number | standard list-name }

Example:

Router(config)# ip extcommunity-list standard NAMED_LIST

Enters IP Extended community-list configuration mode to create or configure an extended community-list.

The example creates a standard named extended community list.

Step 4 

[sequence-number] { deny [regular-expression] | exit | permit [regular-expression] | resequence [starting-sequence] [sequence-increment]}

Example:

Router(config-extcom-list# 100 deny (A-Z)* (a-z)*

Configures an expanded extended community list.

The example creates an expanded extended community list entry with the sequence number 100 that will deny any a route target or route origin pattern that matches any letter.

Step 5 

[sequence-number] {deny [rt extcom-value] [soo extcom-value] | exit | permit [rt extcom-value] [soo extcom-value] | resequence [starting-sequence] [sequence-increment] }

Example:

Router(config-extcom-list)# 1000 permit rt 64512:10 soo 65535:20

Creates an extended community-list and controls access to it.

The example creates a standard named extended community list with a sequence number 1000 that will permit routes from route target 64512:10 and site of origin 65535:20

The route target or site of origin extended community value can be one of the following combinations:

autonomous-system-number : network-number

ip-address : network-number

Step 6 

end

Example:

Router(config-extcom-list)# end

Exits IP Extended community-list configuration mode and enters privileged EXEC mode.

Verifying Extended Community-list Sequences

Perform this task to verify the configuration of extended community-list sequences.

SUMMARY STEPS

1. show ip extcommunity-list [list-number | list-name]

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

show ip extcommunity-list [list-number | list-name]

Example:

Router# show ip extcommunity-list

Displays routes that are permitted by an extended community list.

Configuration Examples for Sequenced Entries in Extended Community-lists

The following examples show how to configure and verify this feature:

Sequenced Extended Community-list Entry Configuration: Example

Resequenced Extended Community-list Entry Configuration: Example

Sequenced Extended Community-list Entry Verification: Example

Sequenced Extended Community-list Entry Configuration: Example

The following example creates and configures a named extended community list that will permit routes only from route target 64512:10, 65000:20, 64535:30, and site of origin 65535:40. All other routes implicitly denied.

Router(config)# ip extcommunity-list standard NAMED_LIST

Router(config-extcom-list)# 1 permit rt 64512:10

Router(config-extcom-list)# 2 permit rt 65000:20

Router(config-extcom-list)# 3 permit rt 64535:30

Router(config-extcom-list)# 4 permit soo 65535:40

Router(config-extcom-list)# end

Resequenced Extended Community-list Entry Configuration: Example

The following example resequences the extended community list entries in the named community list. The first entry is resequenced to the number 50 and the range for each subsequent entry to follow by 100 (for example, 150, 250, 350, etc):

Router(config)# ip extcommunity-list standard NAMED_LIST 
Router(config-extcom-list)# resequence 50 100
Router(config-extcom-list)# end 

Sequenced Extended Community-list Entry Verification: Example

The following example uses the show ip extcommunity-list Exec command to display routes that are permitted by the named extended community list. This example also shows the configuration from the first example after it has been resequence with user-defined values.

Router# show ip extcommunity-list 
Standard extended community-list NAMED_LIST
     50 permit RT:64512:10
     150 permit RT:64512:10
     250 permit RT:64512:10
     350 permit RT:64512:10

Additional References

The following sections provide references related to the BGP Support for Named Extended Community Lists feature.

Related Documents

Related Topic
Document Title

BGP commands

Cisco IOS IP Command Reference, Volume 2 of 4: Routing Protocols, Release 12.3T

BGP configuration tasks

Cisco IOS IP Configuration Guide, Release 12.3

Regular Expressions

"Regular Expressions" appendix of the Cisco IOS Terminal Services Configuration Guide, Release 12.3T


Standards

Standards
Title

No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.


MIBs

MIBs
MIBs Link

No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.

To obtain lists of supported MIBs by platform and Cisco IOS release, and to download MIB modules, go to the Cisco MIB website on Cisco.com at the following URL:

http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml


RFCs

RFCs
Title

No new or modified RFCs are supported by this feature, and support for existing standards has not been modified by this feature.


Technical Assistance

Description
Link

Technical Assistance Center (TAC) home page, containing 30,000 pages of searchable technical content, including links to products, technologies, solutions, technical tips, tools, and lots more. Registered Cisco.com users can log in from this page to access even more content.

TAC Home Page:

http://www.cisco.com/public/support/tac/home.shtml

BGP Support Page:

http://www.cisco.com/cgi-bin/Support/browse/psp_view.pl?p=Internetworking:BGP


Command Reference

This section documents modified commands.

ip extcommunity-list

show ip extcommunity-list

ip extcommunity-list

To create an extended community list to configure Virtual Private Network (VPN) route filtering, use the ip extcommunity-list command in global configuration mode. To delete the extended community list, use the no form of this command.

Global Configuration Mode CLI

ip extcommunity-list expanded-list [ expanded list-name {permit | deny} [regular-expression] | standard-list | standard list-name {permit | deny} [rt value] [soo value] ]

no ip extcommunity-list expanded-list [ expanded list-name | standard-list | standard list-name]

To enter IP Extended community-list configuration mode to create or configure an extended community-list, use the ip extcommunity-list command in global configuration mode. To delete the entire extended community list, use the no form of this command. To delete a single entry, use the no form in IP Extended community-list configuration mode.

ip extcommunity-list expanded-list [expanded list-name | standard-list | standard list-name ]

no ip extcommunity-list expanded-list [expanded list-name | standard-list | standard list-name ]

Expanded IP Extended Community-List Configuration Mode CLI

[sequence-number] deny [regular-expression] [exit | permit [regular-expression] | resequence] [starting-sequence] [sequence-increment]

default {sequence-number | deny [regular-expression] | exit | permit [regular-expression] | resequence [starting-sequence] [sequence-increment]}

no {sequence-number | deny [regular-expression] | permit [regular-expression] | resequence [starting-sequence] [sequence-increment]}

Standard IP Extended Community-List Configuration Mode CLI

[sequence-number] deny [rt value] [soo value] [ exit | permit [rt value] [soo value] | resequence] [starting-sequence] [sequence-increment]

default {sequence-number | deny [rt value] [soo value] | exit | permit [rt value] [soo value] | resequence [starting-sequence] [sequence-increment]}

no {sequence-number | deny [rt value | soo value] | permit [rt value] [soo value] | resequence [starting-sequence] [sequence-increment]}

Syntax Description

expanded-list

An expanded list number from 100 to 500 that identifies one or more permit or deny groups of extended communities.

standard-list

A standard list number from 1 to 99 that identifies one or more permit or deny groups of extended communities.

expanded list-name

Creates an expanded named extended community list and enters IP Extended community-list configuration mode.

standard list-name

Creates a standard named extended community list and enters IP Extended community-list configuration mode.

permit

Permits access for a matching condition.

deny

Denies access for a matching condition.

regular-expression

(Optional) An input string pattern to match against.

rt

(Optional) Specifies the route target (RT) extended community attribute. The rt keyword can be configured only with standard extended community lists and not expanded community lists.

soo

(Optional) Specifies the site of origin (SOO) extended community attribute. The soo keyword can be configured only with standard extended community lists and not expanded community lists.

value

Specifies the route target or site of origin extended community value. This value can be entered in one of the following formats:

autonomous-system-number : network-number

ip-address : network-number

sequence-number

(Optional) The sequence number of a named or numbered extended community list. This value can be a number from 1 to 2147483647.

default

(Optional) Sets a keyword or argument to default behavior or value.

exit

(Optional) Exits from IP Extended community-list configuration mode.

resequence

(Optional) Changes the sequences of extended community list entries to the default sequence numbering or to the specified sequence numbering. Extended community entries are sequenced by ten number increments by default.

starting-sequence

(Optional) Specifies the number for the first entry in an extended community list.

sequence-increment

(Optional) Specifies the increment range for each subsequent extended community entry.


Defaults

Extended community exchange is not enabled by default. It is enabled on a per-neighbor basis with the neighbor send-community command.

Once a permit value has been configured to match a given set of extended communities, the extended community list defaults to an implicit deny for all other values.

Extended community list entries start with the number 10 and increment by ten for each subsequent entry when no sequence number is specified, when default behavior is configured, and when an extended community list is resequenced without specifying the first entry number or the increment range for subsequent entries.

Command Modes

Global configuration
IP Extended community-list configuration

Command History

Release
Modification

12.1

This command was introduced.

12.0(22)S

The maximum number of expanded community list numbers was increased from 199 to 500.

12.2(15)T

The maximum number of expanded community list numbers was increased from 199 to 500.

12.2(25)S

Support for the following was added in Cisco IOS Release 12.2(25)S:

Extended community-list sequencing

IP Extended community configuration mode

Named extended community lists

12.3(11)T

Support for the following was added in Cisco IOS Release 12.3(11)T:

Extended community-list sequencing

IP Extended community configuration mode

Named extended community lists

12.2(27)SBC

This command was integrated into the Cisco IOS Release 12.2(27)SBC.


Usage Guidelines

The ip extcommunity-list command is used to configure named or numbered extended community lists. Extended community attributes are used to filter routes for VPN routing and forwarding instances (VRFs) and Multiprotocol Label Switching (MPLS) Virtual Private Networks (VPNs). All of the standard rules of access lists apply to the configuration of extended community lists. The route target (RT) and site of origin (SOO) extended community attributes are supported by the standard range of extended community lists. Regular expressions are supported in expanded extended community lists. For information about configuring regular expressions, see the Regular Expressions appendix of the Cisco IOS Terminal Services Configuration Guide.

Route Target Extended Community Attribute

The route target (RT) extended community attribute is configured with the rt keyword. This attribute is used to identify a set of sites and VRFs that may receive routes that are tagged with the configured route target. Configuring the route target extended attribute with a route allows that route to be placed in the per-site forwarding tables that are used for routing traffic that is received from corresponding sites.

Site of Origin Extended Community Attribute

The site of origin (SOO) extended community attribute is configured with the soo keyword. This attribute uniquely identifies the site from which the provider edge (PE) router learned the route. All routes learned from a particular site must be assigned the same site of origin extended community attribute, regardless if a site is connected to a single PE router or multiple PE routers. Configuring this attribute prevents routing loops from occurring when a site is multihomed. The SOO extended community attribute is configured on the interface and is propagated into BGP through redistribution. The SOO should not be configured for stub sites or sites that are not multihomed.

IP Extended Community-List Configuration Mode

Named and numbered extended community lists can be configured in IP Extended community-list configuration mode. To enter IP Extended community-list configuration mode, enter the ip extcommunity-list command with either the expanded or standard keyword followed by the extended community list name. This configuration mode supports all of the functions that are available in global configuration mode. In addition, you can perform the following operations:

Configure sequence numbers for extended community list entries

Resequence existing sequence numbers for extended community list entries

Configure an extended community list to use default values

Extended Community List Processing

When multiple values are configured in the same extended community list statement, a logical AND condition is created. All extended community values must match to satisfy an AND condition. When multiple values are configured in separate extended community list statements, a logical OR condition is created. The first list that matches a condition is processed.

Examples

Standard Extended Community-List Configuration Example

In the following example, an extended community list is configured that permits routes from route target 64512:10 and site of origin 65400:20 and denies routes from route target 65424:30 and site of origin 64524:40. List 1 shows a logical OR condition; the first match is processed. List 2 shows a logical AND condition; all community values must match in order for list 2 to be processed.

Router(config)# ip extcommunity-list 1 permit rt 64512:10

Router(config)# ip extcommunity-list 1 permit soo 65400:20

Router(config)# ip extcommunity-list 2 deny rt 65424:30 soo 64524:40

Expanded Extended Community-List Configuration Example

In the following example, an expanded extended community list is configured to deny advertisements from any path through or from autonomous system 65534 from being advertised to the 192.168.1.2 neighbor:

Router(config)# ip extcommunity-list 500 deny _65412_

Router(config)# router bgp 50000

Router(config-router)# address-family vpnv4

Router(config-router-af)# neighbor 172.16.1.1 remote-as 65412

Router(config-router-af)# neighbor 172.16.1.1 neighbor send-community extended

Router(config-router-af)# neighbor 192.168.1.2 remote-as 65534

Router(config-router-af)# neighbor 192.168.1.2 neighbor send-community extended

Router(config-router-af)# end

Named Extended Community-List Configuration Example

In the following example, a named extended community list is configured that will permit routes only from route target 65505:50. All other routes are implicitly denied.

Router(config)# ip extcommunity-list standard NAMED_LIST permit rt 65505:50

IP Extended Community-List Configuration Mode Example

In the following example, an expanded named extended community list is configured in IP Extended community-list configuration mode. A list entry is created with a sequence number 10 that will permit a route target or route origin pattern that matches any network number extended community from autonomous system 65412.

Router(config)# ip extcommunity-list RED 
Router(config-extcom-list)# 10 permit 65412:[0-9][0-9][0-9][0-9][0-9]_ 
Router(config-extcom-list)# exit

Extended Community-List Resequencing Example

In the following example, the first list entry is resequenced to the number 50 and each subsequent entry is configured to increment by 100:

Router(config)# ip extcommunity-list BLUE 
Router(config-extcom-list)# resequence 50 100
Router(config-extcom-list)# exit

Related Commands

Command
Description

export map

Configures an export route map for a VRF.

match extcommunity

Matches a BGP VPN extended community list.

set extcommunity

Sets BGP extended community attributes.

show ip extcommunity-list

Displays routes that are permitted by the extended community list.

show route-map

Displays configured route maps.


show ip extcommunity-list

To display routes that are permitted by an extended community list, use the show ip extcommunity-list command in EXEC mode.

show ip extcommunity-list [list-number | list-name]

Syntax Description

list-number

(Optional) Specifies an extended community list number from 1 to 500. A standard extended community list number is from 1 to 99. An expanded extended list is from 100 to 500.

list-name

(Optional) Specifies an extended community list name.


Defaults

If a specific extended community list number is not specified when the show ip extcommunity-list command is entered, all locally configured extended community lists will be displayed by default.

Command Modes

EXEC

Command History

Release
Modification

12.1

This command was introduced.

12.2(25)S
12.3(11)T

Support for named extended community lists was added. Minor formatting changes were made to the output.

12.2(27)SBC

This command was integrated into the Cisco IOS Release 12.2(27)SBC.


Examples

The following is sample output from the show ip extcommunity-list command in EXEC mode:

Router# show ip extcommunity-list 
Standard extended community-list 1
     10 permit RT:64512:10
     20 permit SoO:65400:20
     30 deny RT:65424:30 SoO:64524:40
Standard extended community-list 99
     10 permit RT:65504:40 SoO:65505:50
     20 deny RT:65406:60 SoO:65307:70
Expanded extended community-list LIST_NAME 
     10 permit 0-9* A-Z* a-z*

Table 1 describes the significant fields shown in the display.

Table 1 show ip extcommunity-list Field Descriptions 

Field
Description

... extended community-list....

The type of extended community-list (standard or expanded), and the name or number of the extended community list.

10

The sequence number of the extended community list entry. 10 is the lowest default sequence number. Extended community lists increment by 10 when default values are configured.

permit/deny

Indicates a permit or deny sequence entry.

RT/SoO

Indicates the route target or the site of origin used in a standard extended community list.

0-9* A-Z* a-z*

Regular expression used in an expanded extended community list.


Related Commands

Command
Description

show route-map

Displays configured route maps.